Method and arrangement for automatically positioning a piston as a function of rotor position in a piston motor

ABSTRACT

Instrument transformers furnish a sinusoidal signal corresponding to the angle of rotation of the crankshaft and a substantially linear signal corresponding to piston position. The difference between the two signals is applied to a phase sensitive detector, whose output activates inlet and outlet valves adding or subtracting hydraulic fluid constituting the linkage between the crankshaft and the piston, depending upon the polarity and magnitude of the output signal from the detector.

United States Patent Kubach et a1. 1 1 Dec. 5, 1972 [54] METHOD AND ARRANGEMENT FOR 3,263,572 8/1966 Sunderland ..91/361 AUTOMATICALLY POSITIONINGA 2,742,763 4/1956 Cohen.... ..60/97 E PISTON AS A FUNCTION 0F ROTOR 2,380,973 8/1945 Kopp ..91/171 POSITION IN A PISTON MOTOR 2,771,845 11/1956 Cagan ..92/138 1,560,492 11/1925 Powell .....60I54.5 R [72] Inventors Hans Kubachi Germ Lem", 3,135,094 6/1964 Kress ..60l54.5 R Fuenh/Bayem, Germany 1,229,443 6/1917 Hall et al. ..92/138 [73] Assgnee: 2225 r r gg' FOREIGN PATENTS OR APPLICATIONS Max Grundig, Fuerth/Bayern, Ger- 1,146,757 7/1960 Germany, ..91/363 A many 674,057 11/1963 Canada .....60/54.5 R Filed" March 20 1970 1,157,876 11/1963 Germany ..60/54.5 R

[21] Appl. No.: 21,418 Primary Examiner-Martin P. Schwadron Assistant ExaminerA. M. Zupcic [30] Foreign Application Priority Data Att0mey M1chael Smker March 22, 1969 Germany ..P 19 14 669.1 [57] ABSTRACT Instrument transformers furnish a sinusoidal signal (gill. ..60/545 R, corresponding to the angle of rotation of the l 58] Fie'ld 363 A crankshaft and a substantially linear signal cor- 91/561 5 /99 l37llol 92/138 responding to piston position. The difference between n the two signals is applied to a phase sensitive detector, [56] References Cited whose output activates inlet and outlet valves adding or subtracting hydraulic fluid constituting the linkage UNITED STATES PATENTS between the crankshaft and the piston, depending upon the polarity and magnitude of the output signal 3,477,346 11/1969 Slavm et a1. ..91/361 from the detector 3,017,865 1/1962 Franz et al..., ..91/361 3,095,784 7/1963 Colhoun ..91/363 A 6 Claims, 13 Drawing Figures 14 [II i 8 O 1 C :9 :1 i: 1+.- h 1 2 I 1 1 5% I 23. -1

2' i L l I PATENTEDnEc 5 I972 SHEET 3 [1F 4 METHOD AND ARRANGEMENT FOR AUTOMATICALLY POSITIONING A PISTON AS A FUNCTION OF ROTOR POSITION IN A PISTON MOTOR BACKGROUND OF THE INVENTION This invention relates to a method and arrangement for automatically positioning the piston of a piston motor relative to the position of the rotary element (crankshaft) of said motor, when the linkage between the piston and the rotary element is a hydraulic one. In this type of motor the connecting rods used in a conventional piston motor between the piston and the crankpin are replaced by a hydraulic system. The piston traveling along a substantially straightline path (translator motion) can thus only be correctly positioned relative to the angular crankshaft position when the amount of fluid within the hydraulic linkage is correct. Thus, the piston position relative to the rotary crankshaft position must be adjusted when the motor is first starting up and, because of leakage in the hydraulic system, possibly also during the operation of the motor.

The position of the piston isnot related to the angle of rotation of the rotary element by a linear function, but follows a substantially sinusoidal curve for a constant change in angle of rotation, that is for a constant angular speed. Thus, to effect a correct positioning of the rotary element, thisrelationship must first be simulated by electrical signals.

SU MMARY OF THE INVENTION This invention constitutes a method for automatically adjusting the position of the piston in a piston motor as a function of the rotary crankshaft position by changing the amount of hydraulic fluid constituting the linkage between said crankshaft and said piston. While the invention is illustrated by use of a motor having a hydraulic linkage between piston and crankshaft, it can, in general terms, be applied to any system wherein the straight-line motion of a first element (piston) is translated, via a hydraulic linkage into corresponding rotational motion of a second element, herein called a rotor. It comprises the steps of generatinga piston position signal having an amplitudevarying as a predetermined function of said piston position relative to a piston reference position. It further comprises the step of generating a rotor position signal corresponding to the angular rotor position relative to a reference rotor position. A difference signal corresponding to the difference between said piston position signal and said rotor position signal is generated and the amount of hydraulic fluid constituting the linkage is varied as a function of said difference signal.

More particularly, the piston position signal is obtained by an instrument transformer whose operation is restricted to furnish a substantially linear output signal as a function of piston position, this linear portion being less than one half a period of the output signal of the instrument transformer. The rotor position signal is also furnished by an instrument transformer. However, in this case, the rotor position signal as a function of rotor position-during a complete cycle of piston operation is a substantially sinusoidal signal. In the event that a difference exists between the rotor position signal and the piston position signal, the difference signal, after processing and suitable circuitry, is caused to open or close inlet and outlet valves controlling the fluid flow to the hydraulic linkage. The valves are operated in accordance with the polarity and the magnitude of the difference signal until such time as the piston position corresponds to the rotor position and the difference signal goes to zero. The instrument transformers furnishing the piston position signal and the rotor position signal may be substantially identical. For example, synchro generators may be used. In this case a mechanical linkage is used to convert the substantially straight line back'and-forth movement of the piston into a bidirectional rotational movement.

The primary excitation of the synchros is furnished by a reference voltage. The amplitudes of the secondary voltages, that is of the output signals, depend upon the position of the rotor and the piston respectively. In order to achieve a comparison of the output signals, it has proven advantageous to use only one phase of the two or more secondary output phases available from the synchro and further, to increase or decrease the primary orsecondary voltages of the synchros in such a manner that the amplitudes of the piston position signals (output voltages) and rotor position signals (output voltages) are equal when the piston and the rotor are in the correct corresponding position. The adjustment of the voltages is necessary, since the two synchros are not driven to the same outputs because of the nonlinear relationship between the rotor position and the piston position, when the same reference voltage is applied to the primaries.

In order to compare the piston position signal and the rotor position signal, that is, to obtain a measure of the difference between the actual position of the piston and its desired position, the rotor position signal may be subtracted from the piston position signal, the resulting difference signal can then be applied to a phase detector and the output of the phase detector is used to control the inlet and outlet valves controlling the hydraulic fluid. If the piston position signal and the rotor position signal are equal, then, of course, the correct positioning between the piston and the rotor has i been achieved.

If the rotor has more than one piston, which often occurs in practice, then a separate instrument transformer is required for each piston, but the same rotor position signal may be used for all pistons. Of course, if the pistons do not all operate in the same phase relationship, then suitable phase correction networks must be supplied.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph showing piston position relative to angular rotor (crankshaft) position.

FIG. 2 shows the amplitude variation of the rotor position signal as a function of rotor angle.

FIG. 3 is a graph showing piston position signal as a function of piston position.

FIG. 4 is a graph showing the output of the phase detector as a function of a difference signal;

FIG. 5 is a block diagram showing the electrical control arrangement in accordance with the present inventron.

FIG. 6 shows the interconnection between the arrangement of FIG. 5 and the controlledmechanical and hydraulic elements, including the mechanical linkage between the piston and the piston synchro shaft.

FIGS. 7a 7g show a number of curves illustrating phase detector output signals for different deviations between the rotor and piston positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the invention will now be discussed with reference to the drawing. I

Also shown in FIG. 6 is the hydraulic coupling 21 linking piston to crank shaft 22 having a journal 23. The amount of fluid 21 isregulated by a valve 18 having an inlet 19 and an outlet 20. The operation of valve 18 is controlled by a difference signal 13, described below. The rotor position signal is derived from a synchrogenerator 7 whose rotor or secondary winding is connected to journal 23.

.The middle curve in FIG. 1 shows the piston movement when the quantity of oil in the hydraulic system is correct, while too much fluid is present in the conditions pictured in the upper curve 2 and too little oil is present under conditions pictured in the lower curve, 3. The limits of the actual piston stroke are indicated by a in FIG. 1 while the available range of piston movement is indicated by V. In this curve the abscissa is the angular position of the rotor (crankshaft) in degrees, while the ordinate shows piston position in centimeters. When the motor is first started, the rotor has an arbitrary position indicated, for example, by b in FIG. 1. Under correct operating conditions, the corresponding piston position is indicated by reference numeral 4. Thus, the piston position should be adjusted tothis point 4 before the operation of themotor commences. Then, during the operation of the motor, the piston will automatically follow the middle curve 1. However, leakage in the system may also cause deviations from curve 1 and require automatic positioning of the piston. The basic arrangement for such piston control is shown in FIG. 5. Synchro generators 7 and 8 are furnished with a primary excitation of a reference voltage U The output of synchro 7, namely the rotor position signal, varies as a function of angular rotor position a as shown in FIG. 2, while the amplitude U,, of the output signal of the synchro 8 depends upon the piston position r, as shown in FIG. 3. Specifically, the output of synchro 7 is shown as curve U, in FIG. 2 while the output of synchro 8, U is restricted to curve U, of FIG. 3 and thus varies only between points 5 and 6 of FIG. 3. The curve U, must be matched to curve U in such a manner that the maximum amplitudes of U,, and U B are equal, since only for those conditions is the nonlinear relationship between the piston position r, and the angular rotor position a as shown in FIG. 1 properly simulated. The adjustment is made by means of a potentiometer 9 which causes a reduction from voltage U, to U, It is shown in FIG. 2 that the maximum amplitude of U coincides with the maximum excursion of U namely points 5 and 6 in FIG. 3.

The mechanical linkage used to restrict the output of the piston position synchro to the range indicated by points 5 and 6 is shown in FIG. 6. Here the piston is designated with reference numeral 15 and the synchro shaft by reference numeral 17. The piston 15 is shown in its upper extreme position corresponding to point 4 in FIG. 1. The lower extreme of its travel is indicated by the dashed lines. It is seen that the mechanical linkage 16 moves through an angle [3 while the piston moves from its top to its bottom extreme positions. The output signal U shown in FIG. 3 thus results from a movement of link 16 through the angle [3 and the corresponding rotation of shaft 17.

The piston position signal and the rotor position signal, that is the outputs of the piston and rotor synchros, are then processed as follows. First, they are interconnected in phase opposition in order that the differencesignal is obtained. This difference signal or more specifically difference voltage is then filtered by a filter 10 which removes undesired harmonics. The filtered output of filter 10 is then applied to a phase sensitive rectifier 11. This phase sensitive rectification is required since both the phase and the magnitude of the piston position signal must coincide with the rotor position signal if correct positioning of the piston relative to the rotor is to be achieved. The reference voltage U which is used for primary excitation of all synchros, is used as a reference phase for the phase sensitive rectifier 11, as shown in FIG. 5. The voltage U.,, available at output 13, has, within a certain region, a sign and amplitude which is directly proportional to the deviation r of the piston from its desired position (see FIG. 4). Thus the output signal U, of detector 11 is a measure whether and how much hydraulic fluid must be added or subtracted from the system.

A detailed example of the functioning of the phase sensitive rectifier is shown in FIG. 7. Here, line a shows the variation of the reference voltage U with time. As a first example, in line b, values of U and U as a function of time are shown wherein U exceeds U Line 0 shows the variation of U, with respect to time when the signals shown in line b are applied to the input of rectifier 11. Further examples of different combinations of variations of U A and U with respect to time are shown in lines d and f of FIG. 7. The corresponding signals at output 13 are shown in lines 2 and g of FIG. 7. Phase sensitive rectifiers operating in this manner are well known in the art and many structures carrying out these functions may be found in the literature.

As shown in FIG. 5, it is also possible to operate a system according to the present invention for controlling a plurality of pistons relative to the rotor. Each piston must of course have a separate means for furnishing a piston position signal, but a single means for furnishing the rotor positionsignal may be used even when a plurality of pistons are present. Thus the additional piston has a synchro 8, a voltage divider or potentiometer 9', its own filter l0 and its corresponding phase sensitive rectifier 11 The same synchro 7 for characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. in a piston engine having a piston and a crank shaft and hydraulic coupling between said piston and said crank shaft, an arrangement for automatically positioning said piston as a function of angular crank shaft position, comprising, in combination, first synchrogenerator means coupled to said piston and having a selected output phase furnishing a piston position signal varying as a predetermined function of the position of said piston relative to a piston reference position; second synchrogenerator means coupled to said crank shaft and having a selected output phase furnishing a rotorposition signal corresponding to the angular crank shaft position relative to a reference crank shaft position; initial adjustment means for adjusting the amplitude of said piston position signal with said rotor position signal in such a manner that, for correct position of said piston, the amplitudes of said signals are equal; connecting means connecting said selected output phase of said first synchrogenerator and said selected output phase of said second synchrogenerator in phase opposition, thereby furnishing a difference voltage; means furnishing a reference voltage; rectifier means having a first input energized by said difference voltage and a second input energized by said reference voltage, and furnishing a phase-dependent difference signal in response thereto; and means for changing the amount of hydraulic pressure medium in said hydraulic coupling in response to said phase-dependent difference signal and to effect the decrease thereof.

2. An arrangement as set forth in claim 1, wherein said first synchro generator means has a shaft; further comprising mechanical linking means linking said piston to said shaft, in such a manner that movement of said piston from a first extreme position to a secondextreme position rotates said shaft of said synchro generator through a predetermined angle less than 7 3. An arrangement as set forth in claim 1, wherein said means for generating a piston position signal comprises means for generating a piston position signal having an amplitude varying as a straight line function of said piston position relative to a reference position.

4. An arrangement as set forth in claim 1, wherein said means for changing the amount of hydraulic pressure medium comprise an inlet valve and an outlet valve.

5. An arrangement as set forth in claim 1, further comprising filter 'means connected between said synchro generators and said phase sensitive rectifier means.

6. An arrangement as set forth in claim 1, wherein said engine has a plurality of pistons, wherein said crankshaft has a plurality of crankpins, each hydraulically coupled to a corresponding one of said pistons; wherein said means for generating a piston-position signal comprises means for generating a plurality of piston-position signals, one for each of said pistons; wherein said comparing means comprise a plurality of comparing means, each for comparing one of said piston-position signals with said rotor-position signal and generating a corresponding plurality of difference signals; and wherein said means for changing the pressure medium comprising means for changing the amount of hydraulic pressure medium coupling a piston to the corresponding crankpin in response to the corresponding difference signal, in such a manner as to minimize said difference signal. 

1. In a piston engine having a piston and a crank shaft and hydraulic coupling between said piston and said crank shaft, an arrangement for automatically positioning said piston as a function of angular crank shaft position, comprising, in combination, first synchrogenerator means coupled to said piston and having a selected output phase furnishing a piston position signal varying as a predetermined function of the position of said piston relative to a piston reference position; second synchrogenerator means coupled to said crank shaft and having a selected output phase furnishing a rotor-position signal corresponding to the angular crank shaft position relative to a reference crank shaft position; initial adjustment means for adjusting the amplitude of said piston position signal with said rotor position signal in such a manner that, for correct position of said piston, the amplitudes of said signals are equal; connecting means connecting said selected output phase of said first synchrogenerator and said selected output phase of said second synchrogenerator in phase opposition, thereby furnishing a difference voltage; means furnishing a reference voltage; rectifier means having a first input energized by said difference voltage and a second input energized by said reference voltage, and furnishing a phase-dependent difference signal in response thereto; and means for changing the amount of hydraulic pressure medium in said hydraulic coupling in response to said phasedependent difference signal and to effect the decrease thereof.
 2. An arrangement as set forth in claim 1, wherein said first synchro generator means has a shaft; further comprising mechanical linking means linking said piston to said shaft, in such a manner that movement of said piston from a first extreme position to a second extreme position rotates said shaft of said synchro generator through a predetermined angle less than 180*.
 3. An arrangement as set forth in claim 1, wherein said means for generating a piston position signal comprises means for generating a piston position signal having an amplitude varying as a straight line function of said piston position relative to a reference position.
 4. An arrangement as set forth in claim 1, wherein said means for changing the amount of hydraulic pressure medium comprise an inlet valve and an outlet valve.
 5. An arrangement as set forth in claim 1, further comprising filter means connected between said synchro generators and said phase sensitive rectifier means.
 6. An arrangement as set forth in claim 1, wherein said engine has a plurality of pistons, wherein said crankshaft has a plurality of crankpins, each hydraulically coupled to a corresponding one of said pistons; wherein said means for generating a piston-position signal comprises means for generating a plurality of piston-position signals, one for each of said pistons; wherein said comparing means comprise a plurality of comparing means, each for comparing one of said piston-position signals with said rotor-position signal and generating a corresponding plurality of difference signals; and wherein said means for changing the pressure medium comprising means for changing the amount of hydraulic pressure medium coupling a piston to the corresponding crankpin in response to the corresponding difference signal, in such a manner as to minimize said difference signal. 